Heretofore, a method for performing separation by use of a clay has been suggested. For example, it is disclosed that the clay is formed into a sheet-like self-standing membrane and can be used as a separation membrane (a clay membrane) (for example, see Patent Document 1). Moreover, a separation method, which uses a clay membrane formed on a base material but which has a purpose of separation of a gas, is disclosed (for example, see Patent Document 2). An example is disclosed in which a 2 μm clay membrane is formed on the base material to separate salt in salt water (for example, see Non-Patent Document 1).
Furthermore, it is reported that the clay membrane is treated to synthesize a mesoporous material (for example, see Patent Documents 3, 4), however a target of this treated clay membrane is a catalyst carrier or the like, and the membrane has large pore diameters, and cannot therefore separate a liquid through pores.    Patent Document 1: JP-A-H06-340413;    Patent Document 2: JP-A-H09-239228;    Patent Document 3: JP-B-3341278;    Patent Document 4: JP-B-3379353; and    Non-Patent Document 1: J. Colloid and Interface Sci. 273 (2004), pp. 540 to 546.